Zero Allocations Fix, main branch (2025.02.24.)

[krasznaa]

Ever since GCC 13 arrived, we've been getting the following runtime errors in our tests:

/usr/include/c++/13/bits/memory_resource.h:76:71: runtime error: null pointer returned from function declared to never return null

Along with a couple of:

/data/ssd-1tb/projects/vecmem/vecmem/tests/core/test_core_terminal_memory_resource.cpp:42:5: runtime error: null pointer passed as argument 2, which is declared to never be null

It was just never the most urgent thing to fix, since the downstream projects don't ask for 0 allocations. :thinking: But as a bit of a palette cleanser, it seemed to be time to do this finally. :thinking: